The surface temperature of the hot roller is monitored with the fusing thermistor and the non-contact thermistor (which is kept at a gap of 1mm from the surface of the hot roller).
If the fusing thermistor temperature becomes greater than 235 °C or the non-contact thermistor temperature becomes greater than 220°C, the CPU cuts off the power to the fusing lamp. At this time, SC543 or SC553 will be generated.
If the thermistor overheat protection fails, there is a thermostat in series with the common ground line of the fusing lamp. If the temperature of the thermostat becomes greater than 185 °C, the thermostat opens, removing power from the fusing lamp. At this time, the machine stops.
[A]: Thermostat: Operation stops when the temperature surrounding the hot roller is more than 185°C.
[B]: Fusing thermistor: SC543 will be generated when the surface temperature of the hot roller is more than 235°C.
[C]: Non-contact thermistor: SC553 will be generated when the surface temperature of the hot roller is more than 220°C.